1. Field of Invention
This invention relates to stents. More particularly, it relates to stents formed from ring elements for providing a highly flexible, low profile stent which is easy to manufacture.
2. Description of the Prior Art
Stents are used as support devices for tubular organs, in particular blood vessels. Current stent devices include the Palmaz Schatz, Boneau, Fontaine, Fogerty, Hilisted, Williams, Gianturco Roubin, Gianturco self-expanding stent, to name some.
U.S. Pat. No. 5,443,498 discloses a vascular stent that includes a continuous wire which is formed into a substantially tubular body having a plurality of oblong, open cells which are staggered around the circumference of the tube. When the tubular stent body is formed in its unexpanded state, the long sides of each oblong cell are arranged substantially parallel to the longitudinal axis of the tubular body. Adjoining cells may then be bonded together at a point between adjacent parallel sides on a cell.
German Patent No. 44 32 938 A1 discloses a tubular or cylindrical shaped endoprosthesis which is applied to a blood vessel by using a balloon catheter. The endoprosthesis consists of a string formed by flexible segments which are substantially arranged in a wave form and in a uniform manner along a helical line.
Conventional zig zag stents have to be rather short because the straight wire segments prevent the stent from easy adaption to curves in the cavities or openings in the patient's body. Furthermore, the expansion forces of customary stents decrease with the length of the stent. An attempt to overcome these drawbacks is the combination of a plurality of short stents connected to one another at their ends. Although these modified stents have better characteristics for certain applications, there is nevertheless still a need for elongated, self-expanding stents which combine the above mentioned characteristics with a better functioning.
Furthermore, a control of the deformation of the stent after self or balloon expansion is strongly desired. U.S. Pat. No. 5,019,090 discloses the manufacturing of a helical stent which consists of wrapping a wire around a cylindrical core in a helical manner. In this case, all segments of the stent have the same length which leads to the drawback that the stent deforms in a undesirable manner after radial compression because the angle bisector of the angle between each pair of segments does not extend parallel to the center axis of the stent. German Patent No. 93 21 136 U1 discloses a way of manufacturing a stent which overcomes this problem and which has the desired feature of a controllable deformation. Finally, it should be noted that all of the above mentioned stents have in common that they are manufactured from a single continuous wire.
From the foregoing, it can be seen that the ideal vascular prosthesis should include several features: easy manufacturing, high flexibility, low profile, little material as possible, radial strength, high expansion rate, firm seating on application instrument, little recoil after expansion, no shortening upon expansion, versatility for use in different anatomies and usable as a balloon and self-expanding stent (depending on use of high or low memory material).